The magazine Obligement published today a benchmark comparison of AmigaOS 4.1 and MorphOS 2.3 running on a Pegasos II. The overall comparisons is based on 20 benchmark categories, which include boot time, processor, 3D, USB, IDE hard disk, WarpOS emulation, 68k emulation, etc. No subjective comparison was made, all benchmarks are based strictly on numbers.
The article was written in French but very easy to understand. You may read it at http://obligement.free.fr/articles/amigaos41_vs_morphos23.php